Tungsten-rhenium alloy powder

ABSTRACT

A PARTICULATE TUNGSTEN-RHENIUM ALLOY POWDER HAVING AN AVERAGE PARTICLE SIZE OF FROM ABOUT 0.5 TO ABOUT 4 MICRONS AND HAVING AN HOMOGENEOUS DISTRIBUTION OF TUNGSTEN AND RHENIUM IN EACH PARTICLE IS DISCLOSED. ADDITIONALLY, A PROCESS FOR PRODUCING THE TUNGSTEN-RHENIUM ALLOY POWDERS IS DISCLOSED. THE PROCESS COMPRISES FORMING AN AQUEOUS SOLUTION OF TUNGSTEN AND RHENIUM SOURCES, SPRAY DRYING SAID SOLUTION AND HEAT TREATING THE RESULTING POWDER UNDER CONTROLLED ATMOSPHERIC AND TEMPERATURE CONDITIONS.

United States Patent 3,623,860 TUNGSTEN-RHENIUM ALLOY POWDER Richard F.Cheney, Harry D. Martin, and Donald S. Parsons, Towanda, Pa., assignorsto GTE Sylvania Incorporated No Drawing. Filed Jan. 6, 1969, Ser. No.789,363 Int. Cl. B22f 9/00; C22b 57/00 US. Cl. 75-.5 AB 5 ClaimsABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION This inventionrelates to tungsten-rhenium alloys. More particularly it relates totungsten-rhenium alloy powders having extremely small particle sizes andhaving a homogeneous tungsten and rhenium distribution throughout theparticles and further relates to processes for producing thesehomogeneous tungsten-rhenium powders.

Heretofore, tungsten-rhenium alloy powders were prepared by mechanicallyblending tungsten powder and rhenium powder in a preselected ratio oftungsten to rhenium. While the composite powder had the correct ratio,for example 95% tungsten and 5% rhenium, the individual particles wereeither tungsten or rhenium. In general, the alloys produced from suchparticles can only be made homogeneous by prolonged sintering andholding the material at elevated temperatures. As can be appreciated,the uniformity of the resulting alloys is dependent to a large degreeupon the uniformity of the blending of the two powders. Another methodused to make powders that are subsequently processed to formtungsten-rhenium alloys is to deposit rhenium in form of a vapor ontotungsten powder. In most instances, the rhenium is more evenlydistributed throughout the tungsten than when mechanical blending isused because most of the particles of tungsten contain some rhenium.However, the homogeneity of the alloy is dependent upon the diffusion ofrhenium into the particle of tungsten. The time required to achieveadequate diffusion during the sintering step can be excessive. Alloyshaving homogeneously distributed low concentrations of either tungstenor rhenium are believed to be unachievable by either of thebeforementioned prior art methods. Additionally, 'both processes useconventional tungsten powders, hence the typical particle sizes of thepowder are from about 4 to about 6 microns (Fisher Sub-Sieve Size). Thetime required for the sintering step of the alloy is longer than wouldbe required if the size of the powder particles were smaller. It is believed, therefore, that a powder having a homogeneous distribution oftungsten and rhenium throughout each particle, regardless of the smallamount of tungsten and rhenium present and that has a smaller particlesize thus reducing the sintering time and improving the uniformity ofthe alloys, would be an advancement in the art.

SUMMARY OF THE INVENTION In accordance with one aspect of thisinvention, there is provided a tungsten-rhenium alloy powder having anaverage particle size of from about 0.5 to about 4 microns (as measuredby Fisher Sub-Sieve Size) and having a homogeneous distribution oftungsten and rhenium throughout each particle. The powder is capable ofbeing processed to the final alloy by conventional powder metallurgytechniques in substantially less time than was required by the prior artprocesses. In accordance with another aspect of this invention there isprovided a method for producing said powders, said method comprising (a)forming an aqueous solution comprising water, a watersoluble tungstensource, and a water-soluble rhenium source, (b) spray drying the aqueoussolution to form tungsten-rhenium alloy powder having the rhenium andtungsten sources relatively homogeneously distributed throughout eachparticle and (c) heat treating the alloy powder under controlledatmospheric and temperature conditions for a time sufficient to convertsaid tungsten and rhenium sources to metallic tungsten and rheniumwithout an appreciable loss of rhenium.

For a better understanding of the present invention, together with otherand further objects, advantages and capabilities thereof, reference ismade to the following disclosure and appended claims in connection withthe above description of some of the aspects of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As previously mentioned, in thepractice of this invention, tungsten and rhenium are relativelyhomogeneously distributed within each individual particle of the powderand the particles of the powder are relatively small, thereby enabling amore rapid sintering of the pow ders to form a homogeneous alloy whencompared with the prior art processes. By relatively homogeneous it ismeant that the percent of tungsten and rhenium in each particle variesless than about :10% by weight from the amount of tungsten and rheniumin the total composition. In most instances it is believed that thevariation is appreciably less than 10%. For example, if a 20:80 rheniumto tungsten alloy is desired, the range in each particle would not varymore than from about 12:88 to about 28:72. Electron-micrographs ofparticles indicate that the particles are completely alloyed, that is,the powder consists of particles that are combined of tungsten andrhenium. X-ray diffraction data also indicate the absence of separatelines for tungsten and for rhenium.

Any water-soluble tungsten source can be used, however, it is preferredto use water-soluble tungsten containing material that can be convertedto tungstic oxide under atmospheric conditions at relatively lowtemperatures, that is below about 300 C. Suitable tungsten sourcesinclude ammonium tungstate and ammonium metatungstate.

Any water-soluble rhenium source can be used. As used herein,water-soluble means that at least 0.1 gram of the material will dissolvein cc. of water at 25 C. Suitable rhenium sources include ammoniumperrhenate, rhenium trichloride, rhenium hexafiuoride and the like.

Materials with a relatively high water solubility are preferred sincethe aqueous solution containing the tungsten and rhenium is subsequentlydried, thus the smallest amount of water that can be employed and stilldissolve the appropriate amounts of tungsten and rhenium is desired inorder to minimize drying costs.

After the aqueous solution containing the tungsten and rhenium sourcesis prepared, the solution is spray dried to form the solid particles.Since the solution containing the tungsten and rhenium sources is ahomogeneous solution, the solid particles formed from that solution arealso homogeneous.

Conventional spray drying techniques can be used, however, since rheniumoxide can be formed during drying, the temperature of the dried materialshould not exceed about 300 C. to avoid rhenium loss. In most instances,therefore, the heating medium used to achieve spray drying should notexceed 300 C. by an appreciable amount. As can be appreciated, theforegoing temperature limitations are under atmospheric pressureconditions. Increased or decreased pressure conditions during the dryingstep can raise or lower the foregoing maximum temperature.

Some rhenium oxides are relatively volatile, however, the rhenium andtungsten sources must be reduced to the metallic form without anappreciable loss of rhenium. Several methods can be used to achieve thereduction without an appreciable rhenium loss. One method is to preheatthe powder in air at about 300 C, for about 2 hours and thereafter thepowder is heated at higher temperatures under a hydrogen atmosphere asin a conventional tungsten oxide reduction process. If desired, however,the particles immediately after spray drying can be heated in a hydrogenatmosphere at about 400 C. for about two hours. The volatile rheniumoxide does not form under these conditions and the powder can thensubsequently be heated in a hydrogen atmosphere at a temperature betweenabout 800 C. and about ll C. to complete the reduction.

Powders containing tungsten and rhenium having essentially any ratio oftungsten to rhenium can be produced. As previously mentioned, theprocess of this invention is particularly advantageous when relativelysmall amounts of tungsten or rhenium are desired in the alloy. It isparticularly desirable to use the process when alloys having a tungstento rhenium weight ratio of greater than 95:5 and less than :95 areproduced. In most instances, tungsten base alloys with the smalleramounts of rhenium will be preferred.

Because the homogeneity of the alloys produced from the powders of thisinvention is improved, the properties of the alloys are also improved.For example, the duetility and bend strength of alloys are improved withimproved homogeneity of the alloy.

To more fully illustrate some of the advantages of this invention, thefollowing non-limiting detailed example is presented. All parts,proportions and percentages are by weight unless otherwise indicated.

EXAMPLE I About 27 parts of ammonium tungstate and about 1 part ofammonium perrhenate are dissolved in about 83 parts of water. The slurryis fed to a conventional spray tower and dried with air having atemperature of below about 300 C. The dried powder is screened to removelumps and a sample of the powder after screening has a particle size offrom about 0.5 to about 2 microns (FSSS).

The powder is heated to about 300 C. for about 2 hours and noappreciable loss of rhenium is noted. The material is then heated toabout ll00 C. in a hydrogen atmosphere for about 5 hours. The powder isthen subjected to a wash of hydrochloric acid and hydrofluoric acid toremove any unconverted rhenium or tungsten compounds.Electron-micrographs of samples of the washed metal powder indicatecompletely alloyed particles, that is, separate crystals of tungsten andrhenium are undetected. Electromicrographs of sample of tungstenrheniumalloy powder produced by the rhenium vapor deposition method clearlyshow separate tungsten and rhenium crystals. Xray diffraction data ofthe washed powder do not show strong patterns for tungsten and rheniumwhereas X-ray patterns for the material produced by the vapor depositiontechniques indicate strong tungsten and rhenium patterns.

Substantially similar results are achieved when the powder after spraydrying is pre-reduced in hydrogen at about 400 C. for about 2 hoursprior to heating to 1100 C. for about 5 hours in a hydrogen atmosphereto complete the reduction. Additionally, the spray dried powder can besubjected to temperatures of 800 C. and ll00 C. in a hydrogen atmospherewithout a loss of rhenium and without any appreciable change in productquality.

After the reduction is complete, the powder can be subjected to standardpowder metallurgical techniques for the production of tungsten products.A high quality alloy is thus produced that exhibits improved propertiesof duetility and bend strength than tungsten-rhenium alloys havingessentially the same elemental analysis but produced by either theblending technique or the vapor deposition technique.

While there have been shown and described what is at present consideredthe preferred embodiments of the invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the scope of the invention as defined bythe appended claims.

We claim:

1. A process for producing a homogeneous tungstenrhenium powder suitablefor powder metallurgy, said method comprising:

(a) forming an aqueous solution comprising water, a water-solubletungsten source and a water-soluble rhenium source;

(b) spray drying said aqueous solution to form a tungsten-rhenium alloypowder having the rhenium and tungsten relatively homogeneouslydistributed throughout each particle, and

(c) heat treating said alloy powder under controlled atmospheric andtemperature conditions for a time sufficient to convert said tungstenand rhenium sources to metallic tungsten and rhenium without anappreciable loss of rhenium.

2. A process according to claim 1 wherein the weight ratio of tungstento rhenium in the final product is less than 5:95.

3. -A process according to claim 1 wherein the weight ratio of tungstento rhenium is greater than 9515.

4. A process according to claim 1 wherein said alloy powder is heated toabout 300 C. for about 2 hours and thereafter is heated to about ll00 C.in a hydrogen atmosphere for about 5 hours.

5. A process according to claim 1 wherein said alloy powder is heated toa temperature of from about 800 C. to about 1100 C. and in a hydrogenatmosphere.

References Cited UNITED STATES PATENTS L. DEWAYNE 'RUTLEDGE, PrimaryExaminer W. W. STALLARD, Assistant Examiner US. Cl. X.R. 84

"UNETED STATES PATE NT OFFECE CER'HFICATE @F CGREflilON Patent No.3,623,860 Dated November 30, 1971 inventor) Richard F. Cheney, Harry D.Martin, Donald S. Parsons It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Col. 1, line 64 in the Specification "small amount" delete "small"Signed and sealed this 23rd day of May 1972.

Attest:

EDWARD T-I.FL1TCEEH,JR. ROBERT GOTTSCHALK Attesti'ng OfficerCommissionerof Patents

